What does it mean to reclaim memory?

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What does it mean when memory is reclaimed? The page table entry is erased? How is memory actually reclaimed? How does memory get allocated?

I understand that you allocate memory via malloc() etc. You get a pointer pointing to the address that's the beginning of your allocated block. When you free and deallocate this memory your pointer no longer points to the address, but the values in the block aren't wiped out. At this point I'm assuming the page table entry gets deleted.

Is that it? What (table, etc.) identifies that there are blocks used and there are blocks free. And when space is actually reclaimed, how is it informed that changes were made to the availability of resources?

For instance, in an exec call how does the heap get reset? The stack I'm assuming just gets reset by resetting the stack pointer.

asked 11 mins ago

Zaphod

875

What does it mean to reclaim memory?